A 24 hour Xbox marathon will work with this twitch achievement, full screen or snapped. Just remember thoigh it doesn't HAVE to be consecutive for the whole hour, just a minute or two watching something on twitch is enough to make the progress bar go further.

I have heard that it does remember what hours you have done and that you don't have to do it in one go.... But since I'm on 78% on this in one stint.... I'm carrying on. Just remember to look back every now and them as streams can go offline, lag or randomly disappear, just go pick another and then carry on. Good luck!!

Good guide

Something else you could add into the solution is that there are some 24/7 streams that will solve the going offline issue. Take a look here.